The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, it is desired that HDDs be able to store more information in their limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles.
In conventional perpendicular magnetic recording media, an oxide is segregated in the grain boundary of magnetic grains in a granular layer, in an attempt to improve the resolution and increase the recording density. In addition, by ensuring that less of the oxide is present in the upper portion than the lower portion of the granular layer, conventional products reduce surface roughness to improve flyability.
Other conventional products include an incoherent switching mode to decrease the switching field of a medium by inserting an exchange coupling layer (ECL) between a cap layer and a granular layer which weakens the exchange coupling between the cap layer and granular layer. In addition, such products explore how the switching field is able to be decreased by imparting a gradation to the granular layer in such a way that the saturation magnetization (Ms) and the anisotropy energy (Ku) thereof reduces from the lower portion to the upper portion of the magnetic grains. In addition, conventional products include means for improving the initial stage growth of the cap layer which allows the thickness of the cap layer to be reduced by decreasing the grain boundary oxide amount on the cap layer side of the granular layer.
A reduction in the size of magnetic clusters which serve as a unit of magnetization switching is essential for achieving higher densification. However, there are inherent problems in conventional products due to the strong lateral exchange coupling of the cap layer, the magnetic cluster size in the recording layer constituted as a combination of the granular layer and a cap layer being larger than the cluster size in the granular layer section. Thus, while a reduction in the thickness of the cap layer has been considered as a means for reducing the magnetic cluster size, when the oxide in the top part of granular layer is reduced in order to reduce the thickness of the cap layer, an increase in the inter-granular exchange coupling of the oxide-reduced granular layer results. In turn, the magnetic cluster size of the granular layer is increased in such a way that, even if the thickness of the cap layer is reduced, the overall cluster size reduction effect in the recording layer cannot be properly produced. Moreover, as capping layer thickness decreases, the granular surface roughness of the medium increases as well, thereby negatively affecting the flyability of the head over the medium. In a layered medium which has a granular layer and a cap layer such as this, a “trade-off” relationship exists, thus hindering the goal of higher densification between the head flyability and the magnetic cluster size of such conventional products.
Thus it would be desirable to achieve both reduced cluster size and decreased surface roughness. However, this goal has heretofore been elusive.